U.S. Pat. No. 3,498,802 discloses the production of materials exhibiting thermoplastic properties by hydrating alkali silicate glass powders of specified compositions. Those glass powders consisted essentially, as expressed in mole percent on the oxide basis, of about 6-20% Na.sub.2 O and/or K.sub.2 O and 80-94% SiO.sub.2, the sum of those components composing at least 90 mole percent of the full composition. Operable optional additions specifically mentioned were PbO, BaO, MgO, B.sub.2 O.sub.3, Al.sub.2 O.sub.3, and ZnO. CaO and Li.sub.2 O were noted as being desirably absent.
The method disclosed involved contacting the glass powders with a gaseous atmosphere containing at least 50% by weight of H.sub.2 O at a pressure of at least one atmosphere and at a temperature commonly within the range of about 100.degree.-200.degree. C. Hydration was continued for a sufficient length of time to produce at least a surface layer on the glass particles containing up to 30% by weight H.sub.2 O. After hydration, the powders were observed to become adhesive and cohesive when heated to temperatures between about 80.degree.-120.degree. C. This phenomenon permitted shaping the particles into bulk bodies utilizing such conventional forming means as pressing, rolling, extrusion, and injection molding.
U.S. Pat. No. 3,912,481 sets forth another method for making alkali metal silicate materials demonstrating forming properties and physical characteristics akin to those possessed by high polymer organic plastics. The method contemplates subjecting glass particles to a two-step process. First, the glass powders are hydrated and, then, second, the powders are partially dehydrated.
Glass compositions operable in that invention consisted essentially, as expressed in mole percent on the oxide basis, of about 3-25% Na.sub.2 O and/or K.sub.2 O and 50-95% SiO.sub.2, the sum of those components constituting at least 55% of the total composition. Optional compatible metal oxides which could advantageously be added to improve melting or forming of the glass and/or to modify the chemical and physical properties of the hydrated glass included Al.sub.2 O.sub.3, B.sub.2 O.sub.3, BaO, CaO, MgO, CdO, PbO, and ZnO. B.sub.2 O.sub.3, CaO, PbO, and ZnO were useful in amounts up to 25%; BaO and Al.sub.2 O.sub.3 were operable in quantities up to 35%; and MgO could be employed in amounts up to 20%. Additions of other optional oxides were preferably maintained below 10%, Li.sub.2 O appeared to inhibit hydration so no more than about 5% could be tolerated.
As noted above, the process described in that patent involved two steps. First, the glass particles were contacted at temperatures above 100.degree. C. with a gaseous H.sub.2 O-containing atmosphere at a H.sub.2 O pressure sufficiently high to secure a saturated or near-saturated environment. The contact was maintained until at least a surface portion of the glass was saturated with H.sub.2 O. The quantity of H.sub.2 O diffused within the glass is a function of the glass composition and, therefore, could vary from less than 5% by weight up to 35% by weight. Second, the water content of the saturated glass is reduced by contacting the hydrated glass at elevated temperatures with a gaseous atmosphere of lower relative humidity. Commonly, the water content was reduced to between about 1-12% by weight, this again depending upon glass composition, such that the glass will contain sufficient water to exhibit thermoplastic characteristics. The method enables the water content in the final glass body to be closely controlled.
United States Application Ser. No. 445,454 filed Feb. 24, 1974 in the names of J. E. Pierson and W. H. Tarcza, abandoned in favor of continuation-in-part Ser. No. 822,877, filed Aug. 8, 1977, describes a single-step process for hydrating glass particles having compositions identical to those operable in U.S. Pat. No. 3,912,481 supra. The inventive method involves contacting the glass particles with gaseous environments having relative humidities varying between about 5-50% at temperatures in excess of 225.degree. C. The water content diffused within the glass, again depending upon glass composition, commonly ranged between about 1-25%. The resultant glass demonstrated thermoplastic properties.
U.S. Pat. No. 3,948,629 delineates yet another process for hydrating fine-dimensioned anhydrous glass bodies. The method involves a single-step process wherein glass particles are hydrated through contact with an acidic aqueous solution, i.e., an aqueous solution containing an acid or salt providing a pH of less than 6. By tailoring the glass composition, the makeup of the hydrating solution, and the temperature and pressure utilized in the hydration reaction, it is possible to closely control the amount of water absorbed into the glass structure. The process is also operable with the anhydrous glass composition recited in U.S. Pat. No. 3,912,481.
Plastics have been generally defined as a group of organic materials which, although stable in use at ambient temperatures, are plastic at some stage of manufacture which permits shaping thereof via the application of heat and/or pressure. Two broad classes of plastics have been recognized: (1) thermoplastic materials, illustrated by vinyl polymers, which are rendered soft and moldable by the application of heat; and (2) thermosetting materials, illustrated by phenol formaldehyde, which are rendered hard by the application of heat.
United States Application Ser. No. 830,603, filed concurrently herewith in the names of A. R. Olszewski and D. R. Parnell, discloses a method for forming anhydrous alkali silicate materials into solid bodies which are hydrated or wherein the silicate structure is depolymerized by protonic reagents. Such bodies may be produced through compression molding the anhydrous alkali silicate materials with water or other protonic reagent at elevated temperatures and high pressures. Other protonic reagents specifically mentioned include NH.sub.4 OH and alcohols.
A very significant characteristic of hydrated glass is the capability of being shaped at much lower temperatures than anhydrous glass of identical composition (excluding, of course, the water diffused therein). Thus, many hydrated glasses can be extruded, compression molded, rolled, or otherwise formed at temperatures and pressures conventionally employed to shape long chain organic plastics. This capability has led to attempts to modify hydrated glasses with organic materials in an effort to impart plastic-like characteristics to glass. Prior work to modify hydrated glasses with organic materials was primarily directed to altering the material before processing. This early work was largely unsuccessful for a number of reasons including the use of inappropriate organic materials, inappropriate glass compositions, improper forming equipment, etc.